Winding currents contain lots of harmonics if motors rotate at the high speed. This paper addresses two key challenges on the harmonic suppression: (1) using the multiple synchronous rotating frame transformations (MSRFTs) to get the primary signals, and (2) proposing the closed-loop detection system (CDS) to extract the harmonics accurately. Firstly, the mathematical model containing the harmonics was built. Secondly, the MSRFTs were introduced, and the high-precision detection method called the CDS was analyzed. The CDS has the higher harmonic detection accuracy than the open-loop method, and can enhance the disturbance rejection capability of the system. Thirdly, the parameter-independent compensation algorithm was proposed to enhance the robustness against the motor parameter variations, which was combined with the compensation calculated by the mathematical model to suppress the harmonics. The effectiveness of the proposed harmonic suppression strategy was verified by the experiments on the turbo molecular pump.

The sensorless drive method of the permanent magnet synchronous motor (PMSM) has attracted wide attention for its low cost and high reliability. As a critical technology, a fast and high-precision rotor position estimation is essential. This work addresses the position estimation deviation issue of the sensorless drive method based on the sliding mode observer (SMO) and phase-locked loop (PLL). A non-linear equivalent model of the SMO is established to analyze and compensate for the position estimation deviation caused by the SMO, and a feed-forward PLL is employed to suppress the steady-state position tracking error under variable speed operation. Firstly, the phase-frequency characteristic of the SMO is obtained by studying the SMO and the switching functions in detail. Then, the analysis of the conventional PLL is carried out in terms of the error transfer function. Besides, the position estimation performance of the feed-forward PLL is discussed with the dynamic error coefficient method. Theoretical analysis and experimental evaluation validated the effectiveness of the proposed position estimation deviation suppression technology of the PMSM combining the phase self-compensation SMO and the feed-forward PLL.

In order to improve the performance of the high-speed brushless direct current motor drives, a novel high-precision sensorless drive has been developed. It is well known that the inevitable voltage pulses, which are generated during the commutation periods, will impact the rotor position detecting accuracy, and further impact the performance of the overall sensorless drive, especially in the higher speed range or under the heavier load conditions. For this reason, the active compensation method based on the virtual third harmonic back electromotive force incorporating the SFF-SOGI-PLL (synchronic-frequency filter incorporating the second-order generalized integrator based phase-locked loop) is proposed to precise detect the commutation points for sensorless drive. An experimental driveline system used for testing the electrical performance of the developed magnetically suspended motor is built. The mathematical analysis and the comparable experimental results have been shown to validate the effectiveness of the proposed sensorless drive algorithm.

In order to improve the performance of surface permanent magnet synchronous motor (PMSM) drives, a novel sensorless drive scheme is proposed in this paper, which is based on the virtual third-harmonic back-EMF incorporating a fraction-N phase-locked loop (FN-PLL) and a synchronous frequency-extract filter (SFF). A simple low-pass filter based circuit is used to obtain the commutation points through the virtual third-harmonic back-EMF. After that, an FN-PLL is applied to catch continuous rotor position angles. On this basis, the SFF-based compensation is proposed to compensate the detecting error adaptively. Meanwhile, the field vector control loop for surface PM motor is proposed, which is based on the proposed rotor position detection link and compensation link. An experimental high-speed magnetically suspended blower platform is built. The effectiveness and the feasibility of the proposed method are validated with experimental results.

This paper investigates the performance optimization of optically pumped magnetometers under zero-field parametric modulation. Based on the analytical solutions of the Bloch equation, both longitudinal and transverse modulations are studied experimentally. To estimate the nonuniform polarization distribution of alkali-metal atoms in the vapor cell, an average pumping rate model is proposed. Furthermore, the accuracy of this model and the measurement of the transverse relaxation rate are verified via the agreement between experimental and theoretical values. The results indicate that optimal performance can be achieved by employing a suitable modulation field, the selection of which is related to the modulation index $u$ in the Bessel series and the pump-light intensity. Although both operating modes show similar responses to weak magnetic fields, their effects on pump-light intensity are different due to the means of detecting atomic polarization. An optimal value of the pump-light intensity on the response strength exists in longitudinal modulation. However, with regard to transverse modulation, the sensitivity under weak pump-light intensity is better. This research has far-reaching significance for cases when the parametric modulation is manipulated.